The transcription factors SMAD2 and SMAD3 are the effectors of classical transforming growth factor beta (TGFβ) signalling. This signalling cascade is involved in many cellular processes including proliferation and differentiation and is known to be a potent inhibitor of myogenic differentiation through SMAD3. We have previously shown that retinoic acid (RA) can upregulate SMAD3 in models of adipogenesis and mesenchymal stem cells and that SMAD3 can interact with the bZIP transcription factor C/EBPβ to disrupt its DNA binding. Forced expression of C/EBPβ inhibits myogenic differentiation but the mechanism has not been fully elucidated. Herein we show that RA increases Smad3 expression in myoblasts and that RA treatment antagonizes TGFβ-mediated inhibition of myogenic differentiation. TGFβ treatment increased C/EBPβ expression which was reversed by RA treatment. Further, RA was able to disrupt C/EBPβ occupancy of the Pax7 and Smad2 promoters in myoblasts. Loss of C/EBPβ in primary myoblasts using a conditional knockout model partially protected these cells from the anti-myogenic effects of TGFβ treatment. The TGFβ effector protein SMAD2 is expressed in myoblasts but its specific function in myogenesis has not been determined, as Smad2 knockout models are embryonic lethal. Thus, we created a novel Smad2 conditional knockout model where Smad2 is excised in PAX7-expressing muscle satellite cells. Herein we demonstrate a role for SMAD2 specifically in myogenic fusion. We describe a regeneration defect after acute injury and decreased fiber cross-sectional area at P21 (post-natal day 21) in Smad2cKO muscle, without affecting the numbers of PAX7-positive cells. Further, we reveal a mechanism whereby SMAD2 regulates KLF4 expression and mediates the KLF4-induced increased of the fusion gene Npnt. This work describes the pro-myogenic actions of RA-induced SMAD3 and the novel function of SMAD2 in terminal myogenic differentiation and fusion. This work also discusses future directions, implications and new insights into non-canonical SMAD actions.

A feature of neoplastic cells is that mutations in the key intermediates of TGF-β signaling contribute to the loss of sensitivity to its anti-tumor effects. The role of SMAD3 and SMAD4 germline mutations in breast cancer predisposition is currently unclear. To address this, mutation analysis of the Mad-Homology 2 domains in 408 breast cancer cases and 710 controls recruited by the Breast Cancer Family Registry (BCFR) was performed using Denaturing High-Pressure Liquid Chromatography. This study identified 23 distinct intronic variants, and three coding variants c.1214T>C, c.1478G>A, and c.1701A>G in SMAD4. No aberrant splicing was observed, but qPCR analysis and tissue expression data showed significantly elevated SMAD3 expression relative to controls (p<0.05). For SMAD4, c.1478G>A from a familial breast cancer case showed a 5-fold expression change. Taken together, inactivating alterations are not driving tumorigenesis. Rather, aberrant germline expression provides novel insight into SMAD3 and SMAD4’s roles in breast cancer predisposition.

A feature of neoplastic cells is that mutations in the key intermediates of TGF-β signaling contribute to the loss of sensitivity to its anti-tumor effects. The role of SMAD3 and SMAD4 germline mutations in breast cancer predisposition is currently unclear. To address this, mutation analysis of the Mad-Homology 2 domains in 408 breast cancer cases and 710 controls recruited by the Breast Cancer Family Registry (BCFR) was performed using Denaturing High-Pressure Liquid Chromatography. This study identified 23 distinct intronic variants, and three coding variants c.1214T>C, c.1478G>A, and c.1701A>G in SMAD4. No aberrant splicing was observed, but qPCR analysis and tissue expression data showed significantly elevated SMAD3 expression relative to controls (p<0.05). For SMAD4, c.1478G>A from a familial breast cancer case showed a 5-fold expression change. Taken together, inactivating alterations are not driving tumorigenesis. Rather, aberrant germline expression provides novel insight into SMAD3 and SMAD4’s roles in breast cancer predisposition.

The incidence of cardiovascular disease has reached epidemic proportions in North America. Specifically, myocardial infarctions (MI) are a major contributor to heart failure which greatly influences morbidity and mortality rates in developed nations. In the post-MI heart, cardiac fibroblasts migrate to the damaged area, convert to myofibroblasts and contribute to infarct scar contraction. As well, cardiac myofibroblasts are hypersynthetic for matrix components eg, collagen, and de novo production of fibrillar collagens lessens the chance for acute scar rupture. TGF-1 is important in the initiation of cardiac healing and fibrosis. Canonical TGF-1 signaling occurs with the activation of receptor-operated Smads (R-Smads) including Smad3. The current study addresses the question of whether Smad3 and/or myocardin influence myofibroblast contractility. We believe that myocardin is a Smad3 binding partner and cofactor and thus contributes to Smad associated healing and fibrotic events in the heart. In mesenchyme-derived cells, myocardin exists as a nuclear protein and is a cardiac and smooth muscle specific transcriptional coactivator of serum response factor (SRF). This transcription factor has been shown to bind to Smad3 in COS-7 cells (a green monkey kidney fibroblast-like cell line) and we suggest that it may contribute to fibroproliferative events. Precisely how Smad3/myocardin facilitates post-MI wound healing and/or contributes to inappropriate post-MI fibrosis is unknown. Very little work has been done to address myocardin expression in cardiac ventricular myofibroblasts. While a number of previous studies address TGF-β/Smad signaling in cardiac myofibroblasts, none have addressed the effects of overexpressed Smad3 on cellular contractility and collagen secretion. As Smad3 and its endogenous inhibitor Smad eg, I-Smad7, contribute significantly to TGF-β signaling in myofibroblasts, we rationalize that they must be important in the regulation of many fibroproliferative processes. Our goals were first to measure/determine myocardin expression in primary ventricular myofibroblasts; second, to explore a putative interaction between Smad3 and myocardin; third to examine a possible link between TGF-β1 stimulation, myocardin and Smad3. Finally, we sought to examine the effect of overexpressed Smad3, Smad7 and myocardin on contractility and collagen production. These experiments were conducted by using RT-PCR, co-immunoprecipitation, adenoviral overexpression of Smad3, Smad7 and myocardin, Western blot analysis, collagen gel deformation assays (contractility studies) and finally, Pro-collagen 1 N-terminal Peptide (P1NP) secretion as a measure of mature collagen production. We document the novel expression of myocardin in ventricular myofibroblasts and provide evidence that myocardin may serve as a Smad3 cofactor in cardiac myofibroblasts. Further, myocardin overexpression is linked to increased contractility in myofibroblasts compared to LacZ infected controls, and that TGF-β1 acutely stimulated myocardin expression followed by a dramatic reduction 1 hour thereafter. Overexpressed Smad3 alone led to increased contractility in primary ventricular myofibroblasts. Thus the effect of increasing myocardin expression had a comparable effect to that of increased Smad3 alone with this endpoint. Finally, overexpression of both Smad3 and myocardin in the presence of TGF-β1 led to an additive stimulation of contractility in cells when compared to the effect of TGF-β1 stimulation alone. Overexpressed Smad7 alone was associated with decreased secretion of type I collagen when compared to the control; when cells overexpressing Smad7 are stimulated with TGF-β1, collagen secretion is dramatically reduced when compared to cells treated with TGF-β1. In an addition series of experiments we addressed reverse mode NCX1 function as a means of Ca2+ entry to the cytosol of myofibroblasts upon their excitation. We have previously shown the stimulatory effect of TGF-β1 on myofibroblast contractility, and we now report that overexpression of Smad3 alone led to increased mRNA expression of NCX1. Thus it is possible that TGF-β1 signaling via Smad3 may influence Ca2+ movements and thus contractile performance in ventricular myofibroblasts. / May 2008

The incidence of cardiovascular disease has reached epidemic proportions in North America. Specifically, myocardial infarctions (MI) are a major contributor to heart failure which greatly influences morbidity and mortality rates in developed nations. In the post-MI heart, cardiac fibroblasts migrate to the damaged area, convert to myofibroblasts and contribute to infarct scar contraction. As well, cardiac myofibroblasts are hypersynthetic for matrix components eg, collagen, and de novo production of fibrillar collagens lessens the chance for acute scar rupture. TGF-1 is important in the initiation of cardiac healing and fibrosis. Canonical TGF-1 signaling occurs with the activation of receptor-operated Smads (R-Smads) including Smad3. The current study addresses the question of whether Smad3 and/or myocardin influence myofibroblast contractility. We believe that myocardin is a Smad3 binding partner and cofactor and thus contributes to Smad associated healing and fibrotic events in the heart. In mesenchyme-derived cells, myocardin exists as a nuclear protein and is a cardiac and smooth muscle specific transcriptional coactivator of serum response factor (SRF). This transcription factor has been shown to bind to Smad3 in COS-7 cells (a green monkey kidney fibroblast-like cell line) and we suggest that it may contribute to fibroproliferative events. Precisely how Smad3/myocardin facilitates post-MI wound healing and/or contributes to inappropriate post-MI fibrosis is unknown. Very little work has been done to address myocardin expression in cardiac ventricular myofibroblasts. While a number of previous studies address TGF-β/Smad signaling in cardiac myofibroblasts, none have addressed the effects of overexpressed Smad3 on cellular contractility and collagen secretion. As Smad3 and its endogenous inhibitor Smad eg, I-Smad7, contribute significantly to TGF-β signaling in myofibroblasts, we rationalize that they must be important in the regulation of many fibroproliferative processes. Our goals were first to measure/determine myocardin expression in primary ventricular myofibroblasts; second, to explore a putative interaction between Smad3 and myocardin; third to examine a possible link between TGF-β1 stimulation, myocardin and Smad3. Finally, we sought to examine the effect of overexpressed Smad3, Smad7 and myocardin on contractility and collagen production. These experiments were conducted by using RT-PCR, co-immunoprecipitation, adenoviral overexpression of Smad3, Smad7 and myocardin, Western blot analysis, collagen gel deformation assays (contractility studies) and finally, Pro-collagen 1 N-terminal Peptide (P1NP) secretion as a measure of mature collagen production. We document the novel expression of myocardin in ventricular myofibroblasts and provide evidence that myocardin may serve as a Smad3 cofactor in cardiac myofibroblasts. Further, myocardin overexpression is linked to increased contractility in myofibroblasts compared to LacZ infected controls, and that TGF-β1 acutely stimulated myocardin expression followed by a dramatic reduction 1 hour thereafter. Overexpressed Smad3 alone led to increased contractility in primary ventricular myofibroblasts. Thus the effect of increasing myocardin expression had a comparable effect to that of increased Smad3 alone with this endpoint. Finally, overexpression of both Smad3 and myocardin in the presence of TGF-β1 led to an additive stimulation of contractility in cells when compared to the effect of TGF-β1 stimulation alone. Overexpressed Smad7 alone was associated with decreased secretion of type I collagen when compared to the control; when cells overexpressing Smad7 are stimulated with TGF-β1, collagen secretion is dramatically reduced when compared to cells treated with TGF-β1. In an addition series of experiments we addressed reverse mode NCX1 function as a means of Ca2+ entry to the cytosol of myofibroblasts upon their excitation. We have previously shown the stimulatory effect of TGF-β1 on myofibroblast contractility, and we now report that overexpression of Smad3 alone led to increased mRNA expression of NCX1. Thus it is possible that TGF-β1 signaling via Smad3 may influence Ca2+ movements and thus contractile performance in ventricular myofibroblasts.

La compréhension des mécanismes impliqués dans la formation des métastases est l’un des défis majeurs de la recherche sur le cancer. En effet, la formation de métastases est la cause principale de mortalité chez les patients atteints du cancer. L'influence du microenvironnement tumoral fait partie intégrante de la recherche et plusieurs études démontrent qu’il joue un rôle primordial dans l’invasion des cellules tumorales. L’une des caractéristiques du microenvironnement tumoral est l’hypoxie. Les cellules cancéreuses ont développé différentes stratégies afin de survivre dans ce microenvironnement. Des études récentes rapportent que des mécanismes posttranscriptionnels sont induits par l’hypoxie tels que le routage intracellulaire de molécules d'adhésion, de protéases et l’activation de facteurs de croissance, et qu’ils influencent le phénotype métastatique des cellules cancéreuses. L’étape importante dans l’initiation de la formation des métastases est la dégradation de la membrane basale de la tumeur et de la matrice extracellulaire. Les cellules cancéreuses ont développé des stratégies afin de faciliter leur migration dont l’une est la formation d'invadopodes. Malgré plusieurs études sur la biogenèse et les fonctions de ces structures, peu de travaux ont été accomplis concernant l’influence du microenvironnement tumoral hypoxique sur la formation et les fonctions des invadopodes. Les travaux présentés dans cette thèse portent sur l’étude des mécanismes induits par l’hypoxie dans l’invasion des cellules cancéreuses. Dans le premier chapitre de la section résultats, nous démontrons que l’hypoxie induit une relocalisation stratégique de la furine, une convertase de pro-protéines, dans une boucle de recyclage en périphérie cellulaire. Nous démontrons que la redistribution de la furine favorise l’invasion cellulaire en condition hypoxique. Dans le deuxième chapitre, nous avons étudié l'impact de la relocalisation de la furine en hypoxie sur la maturation de substrats tumorigéniques. Nos résultats indiquent que l’hypoxie favorise la maturation du TGFß par la furine dans des vésicules acides. Nous démontrons que la présence d’une histidine, sensible au pH, située au site de clivage du pro-TGFß par la furine influence la capacité de cette dernière à cliver la pro-protéine. Enfin, dans le dernier chapitre, nous démontrons que l’induction hypoxique de la formation des invadopodes est principalement causée par la signalisation dépendante de Smad3 du TGFß. Nous identifions la HDAC6 comme étant un régulateur de la signalisation du TGFß en hypoxie. La HDAC6 permettrait la libération de Smad3 du réseau de tubuline, et suite à la liaison du TGFß sécrété à son récepteur, permettrait la phosphorylation et la translocation nucléaire de Smad3 afin d'induire ses gènes cibles. L'ensemble de ces travaux a permis d'identifier des molécules clés impliquées dans la formation des invadopodes en condition hypoxique. Nos travaux ont contribué de manière substantielle à nos connaissances des mécanismes impliqués dans l’invasion cellulaire dans le microenvironnement hypoxique. Nos résultats permettront en outre l’identification de cibles thérapeutiques potentielles qui pourraient servir à inhiber l’invasion cellulaire et la formation de métastases.

The incidence of cardiovascular disease has reached epidemic proportions in North America. Specifically, myocardial infarctions (MI) are a major contributor to heart failure which greatly influences morbidity and mortality rates in developed nations. In the post-MI heart, cardiac fibroblasts migrate to the damaged area, convert to myofibroblasts and contribute to infarct scar contraction. As well, cardiac myofibroblasts are hypersynthetic for matrix components eg, collagen, and de novo production of fibrillar collagens lessens the chance for acute scar rupture. TGF-1 is important in the initiation of cardiac healing and fibrosis. Canonical TGF-1 signaling occurs with the activation of receptor-operated Smads (R-Smads) including Smad3. The current study addresses the question of whether Smad3 and/or myocardin influence myofibroblast contractility. We believe that myocardin is a Smad3 binding partner and cofactor and thus contributes to Smad associated healing and fibrotic events in the heart. In mesenchyme-derived cells, myocardin exists as a nuclear protein and is a cardiac and smooth muscle specific transcriptional coactivator of serum response factor (SRF). This transcription factor has been shown to bind to Smad3 in COS-7 cells (a green monkey kidney fibroblast-like cell line) and we suggest that it may contribute to fibroproliferative events. Precisely how Smad3/myocardin facilitates post-MI wound healing and/or contributes to inappropriate post-MI fibrosis is unknown. Very little work has been done to address myocardin expression in cardiac ventricular myofibroblasts. While a number of previous studies address TGF-β/Smad signaling in cardiac myofibroblasts, none have addressed the effects of overexpressed Smad3 on cellular contractility and collagen secretion. As Smad3 and its endogenous inhibitor Smad eg, I-Smad7, contribute significantly to TGF-β signaling in myofibroblasts, we rationalize that they must be important in the regulation of many fibroproliferative processes. Our goals were first to measure/determine myocardin expression in primary ventricular myofibroblasts; second, to explore a putative interaction between Smad3 and myocardin; third to examine a possible link between TGF-β1 stimulation, myocardin and Smad3. Finally, we sought to examine the effect of overexpressed Smad3, Smad7 and myocardin on contractility and collagen production. These experiments were conducted by using RT-PCR, co-immunoprecipitation, adenoviral overexpression of Smad3, Smad7 and myocardin, Western blot analysis, collagen gel deformation assays (contractility studies) and finally, Pro-collagen 1 N-terminal Peptide (P1NP) secretion as a measure of mature collagen production. We document the novel expression of myocardin in ventricular myofibroblasts and provide evidence that myocardin may serve as a Smad3 cofactor in cardiac myofibroblasts. Further, myocardin overexpression is linked to increased contractility in myofibroblasts compared to LacZ infected controls, and that TGF-β1 acutely stimulated myocardin expression followed by a dramatic reduction 1 hour thereafter. Overexpressed Smad3 alone led to increased contractility in primary ventricular myofibroblasts. Thus the effect of increasing myocardin expression had a comparable effect to that of increased Smad3 alone with this endpoint. Finally, overexpression of both Smad3 and myocardin in the presence of TGF-β1 led to an additive stimulation of contractility in cells when compared to the effect of TGF-β1 stimulation alone. Overexpressed Smad7 alone was associated with decreased secretion of type I collagen when compared to the control; when cells overexpressing Smad7 are stimulated with TGF-β1, collagen secretion is dramatically reduced when compared to cells treated with TGF-β1. In an addition series of experiments we addressed reverse mode NCX1 function as a means of Ca2+ entry to the cytosol of myofibroblasts upon their excitation. We have previously shown the stimulatory effect of TGF-β1 on myofibroblast contractility, and we now report that overexpression of Smad3 alone led to increased mRNA expression of NCX1. Thus it is possible that TGF-β1 signaling via Smad3 may influence Ca2+ movements and thus contractile performance in ventricular myofibroblasts.

TGF-β/Activin/Nodal 信號通路調節了許多重要的細胞生物學過程,例如,細胞分裂,增殖,分化,遷移和衰老凋亡。此外,它也在胚胎髮育,損傷修復,腫瘤發生,組織纖維化,糖尿病發生及其免疫方面也扮演了重要的角色。TGF-β家族信號分子,包括TGF-β, Activin 和 Nodal,通過結合到它們各自的受體從而啟動它們,而啟動後的受體又可以通絡磷酸化作用進一步激活Smad2 和Smad3 蛋白,激活後的Smad2 和Smad3 蛋白可以和Smad4 蛋白形成複合體,一起從細胞膜轉移到細胞核內調節下游基因的表達。 / 在人的胚胎幹細胞中,TGF-β/Activin/Nodal signaling 做為最關鍵的信號分子,調節了人胚胎幹細胞的自我更新以及胚胎幹細胞多能性的維持。而在小鼠胚胎幹細胞中,該信號通路的功能並沒有清楚的研究。在本論文中,我們分離以及建立了Smad3 突變體的小鼠胚胎幹細胞系(Smad3-/-),該突變體細胞能夠維持正常小鼠胚胎幹細胞的形態,在自我增殖更新方面也沒有缺。此外,幹細胞多能性相關的標記基因以及組織標記基因表達水準也與野生型細胞非常相似,但是,在擬胚體的生長過程中,Smad3 被敲除後導致了組織發育相關的標記基因出現了差異性的表達。與野生型相比,中胚層標記基因（T 和GSC）的表達明顯受到了抑制。另外令人驚奇的是,將Smad3 基因敲除的胚胎幹細胞皮下注射裸鼠後長出了惡性的未完全成熟的畸胎瘤,而野生型的幹細胞則更傾向于長成成熟的良性畸胎瘤。進一步的分析發現,Smad3 功能性缺失後,細胞的增殖速率明顯增加了;紫外(UV)誘變後,相對於野生型,突變體細胞的抗凋亡能力也明顯增強了;並且在分化過程中,突變體細胞的遷移能力也要明顯強于野生型細胞。所有以上的細胞特徵可以解釋為什麼Smad3 基因敲除後會長出惡性的畸胎瘤。 / Microarray 分析結果發現,一個DNA 損傷修復基因Rif1,在Smad3 突變體細胞中呈現出了很高的上調,這個基因的上調現象已經發現是和侵蝕性腫瘤的發生是相關的,而且該基因的上調水準也與乳腺癌的浸潤程度是非常相關的。染色質免疫共沉澱和螢光素酶活性實驗進一步證實了Smad3 可以結合到Rif1 的啟動子領域從而直接抑制該基因的表達。這些實驗進一步說明了Smad3 可能通過下調Rif1 基因的表達,從而抑制了小鼠胚胎幹細胞長出惡性畸胎瘤的發生。 / 總之,我們建立了Smad3-/-基因敲除的小鼠胚胎幹細胞系,並且發現該突變體細胞傾向于長出惡性的畸胎瘤。我們推測,在正常的情況下,Smad3 正是通過抑制了DNA 損傷修復因數基因Rif1 的表達,從而阻止了惡性畸胎瘤的發生。這些研究的結果不僅開闊了我們對於惡性腫瘤發生的認識,而且為我們在幹細胞或誘導多能幹細胞治療應用中防止畸胎瘤的發生提供了新的思路和策略。 / TGF-β/Activin/Nodal signaling controls many important biological procedures in cells, such as cell division, proliferation, differentiation, migration and apoptosis in mammalian cells. It also plays a critical role in embryo development, wound healing, tumorigenesis, tissue fibrosis, diabetes and immunity. TGF-β superfamily ligands, such as TGF-β, Activin and Nodal bind to their respective ligand receptors and activate them, which in turn activate the receptor related SMAD proteins by phosphorylation, including Smad2 and Smad3. Once phosphorylated, they can cooperate with Smad4 and enter nucleus to bind promoter DNA sequence and regulate the target gene expression. / In human embryonic stem (ES) cells, TGF-β/Activin/Nodal signaling has been demonstrated to be the most critical pathways for ES cell self-renewal and maintenance of undifferentiated state. However, in mouse ES cells, its role is yet to be clearly exploited. In this study, we reported the derivation and establishment of mouse Smad3 knockout embryonic stem cell lines (Smad3-/- ES cells). Smad3-/- ES cells maintain normal ES cell morphology and express higher level of mouse ES cell markers, alkaline phosphatase (AP) and stage-specific embryonic antigen 1(SSEA1), and display no defect on self-renewal capacity. In addition, both of them show similar expression profiles of pluripotent and lineage marker genes compared to wild type ES cells. However, Smad3 ablation results in transient different expression of germ layer markers during embryoid body (EB) development. The expression of mesoderm lineage marker, like T and GSC, is significantly reduced in the EBs developed by Smad3-/- ES cells compared to EBs formed by wild type ES cells. More interestingly, to investigate the differentiation potential of Smad3-/- ES in vivo, we subcutaneously injected both wild type and Smad3-/- ES cells into nude mice, and observed that Smad3-/- ES cells are prone to grow malignant immature teratomas, while wild type ES cells develop normal mature teratomas. Further characterization of Smad3-/- ES cells demonstrates that depletion of Smad3 increases ES cell proliferation; Smad3-/- ES cells show higher capacity of the anti-apoptosis after UV irradiation and the migration potential of Smad3-/- ES cell differentiated cells is enhanced compared to wild type ES cells in the wound healing assay. Therefore, Smad3-/- ES cells exhibit enhanced malignancy, which may underlie their teratoma malignancy. / Microarray analysis shows that Rif1, a DNA repair factor is highly upregulated in Smad3-/- ES cells. Upregulation of DNA repair factor is found to be associated with invasive tumor. And the expression level of Rif1 is linked to the invasive degree of breast cancer at certain level. Chromatin immunoprecipitation (ChIP) assay and luciferase assay confirm that Smad3 binds to Rif1 promoter region and directly represses its expression; knockdown Rif1 in Smad3-/- ES cells rescues the expression level of Ccnd2 and migration potential to wild type ES cell level. Taken together, all these data suggests that Smad3 may suppress the malignancy of mouse embryonic stem cell formed teratoma through downregulating Rif1 expression in normal condition. / In summary, we reported the establishment of Smad3-/- ES cells and characterization of these cells. We discovered that Smad3-/- ES cells are prone to grow malignant teratomas compared to wild type ES cells. We hypothesized that Smad3 may suppress the malignancy of teratoma through repressing a DNA repair factor, Rif1. This information will not only broaden our general knowledge of malignant teratomas, but also help us to develop strategies to prevent malignant teratoma formation in ES/iPS cell therapy. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Li, Peng. / Thesis (Ph.D.) Chinese University of Hong Kong, 2014. / Includes bibliographical references (leaves 149-181). / Abstracts also in Chinese.

Medulloblastoma (MB) is the most common pediatric malignant brain tumor. Little is known about aggressive forms of this disease. In order to identify pathways mediating aggressiveness in MB, we performed microarray experiments. Primary human MBs were compared to their patient matched recurrent or metastatic counterparts. Murine tumors from two MB mouse models that present with differing clinical severities were also evaluated. We identified the Transforming Growth Factor-beta (TGF-β) as a potential contributor to MB pathogenesis in both species. Smad3, a major downstream component of the TGF-β pathway, was shown to correlate with MB metastasis and survival in human tissue. Similarly, Smad3 expression during development identified a subset of cerebellar neuronal precursors as putative cells of origin for the Smad3 positive MBs. To our knowledge, this is the first study that links TGF-β to MB pathogenesis. Our research suggests that canonical activation of this pathway leads to better prognosis for patients.

Medulloblastoma (MB) is the most common pediatric malignant brain tumor. Little is known about aggressive forms of this disease. In order to identify pathways mediating aggressiveness in MB, we performed microarray experiments. Primary human MBs were compared to their patient matched recurrent or metastatic counterparts. Murine tumors from two MB mouse models that present with differing clinical severities were also evaluated. We identified the Transforming Growth Factor-beta (TGF-β) as a potential contributor to MB pathogenesis in both species. Smad3, a major downstream component of the TGF-β pathway, was shown to correlate with MB metastasis and survival in human tissue. Similarly, Smad3 expression during development identified a subset of cerebellar neuronal precursors as putative cells of origin for the Smad3 positive MBs. To our knowledge, this is the first study that links TGF-β to MB pathogenesis. Our research suggests that canonical activation of this pathway leads to better prognosis for patients.